The screw-up became one of the most memorable moments in Academy Awards history.

The 89th annual Academy Awards was mere minutes from wrapping a somewhat boring broadcast when backstage staffers started running to the microphone to interrupt the final acceptance speeches.

Presenters Warren Beatty and Faye Dunaway had just awarded the Oscar for Best Picture to “La La Land.” The only problem was they were supposed to give “Moonlight” that honor, and there had been a terrible mix-up behind the scenes.

The veteran actors took to the stage to present the final award of the night. As Beatty read the card in the envelope, he looked visibly confused. He checked the envelope more than once, paused, looked to Dunaway, started to announce the winner, and then passed the envelope to his co-presenter, who promptly said, “La La Land.”

“As the ‘La La Land’ cast was taking the stage to celebrate, a stagehand in the wings said, ‘Oh ... Oh my god, he got the wrong envelope.’ They walked back and forth repeating it.”

Only two humans on the planet know the Oscar winners in advance, and that’s PricewaterhouseCoopers’ Brian Cullinan and Martha Ruiz. After stuffing the envelopes and locking them in a briefcase, they memorize the list of winners. Just last week, the duo blogged on The Huffington Post about the process, and described a meticulous system for ensuring there were no mistakes:

“We hand each envelope directly to the presenter in each category. We are positioned on either side of the stage, so we can hand envelopes from stage right or stage left, depending on where the presenter is entering. We don’t leave for the entire show ― not even for a bathroom break! We’re so focused on doing our jobs that we don’t mind the hours of standing.”

In the photo below, Cullinan appears to be checking envelopes with a stagehand as “La La Land” producer Fred Berger thanked his family.

The producers and cast of “Moonlight” were invited to the stage as the stunned crowd applauded and host Jimmy Kimmel joked about the blunder. Beatty took to the microphone to explain what went wrong:

“I want to tell you what happened. I opened the envelope and it said Emma Stone, ‘La La Land.’ That’s why I took such a long look at Faye and at you. I wasn’t trying to be funny.”

Kimmel elaborated on Beatty’s confusion in an interview with ABC.

“I know that the envelope Warren Beatty was handed said ‘Outstanding Female Actor’ on it,” Kimmel said. “This was confusing, obviously. We thought he was being coy and cute and milking it to make everybody suffer, but in reality, he was perplexed by why her name was on it.”

Emma Stone was also confused by the mix-up, as she told reporters backstage that she was holding her winning envelope when Dunaway announced the Best Picture winner, suggesting that she didn’t understand how Beatty’s card could have been the same.

The accounting firm vowed to investigate how the mistake occurred. Meanwhile, the cast and crew of “Moonlight” celebrated their surreal win.

“It’s very hard to feel joy in a moment like that,” Mahershala Ali, who won Best Supporting Actor for his work in “Moonlight,” told the Hollywood Reporter. “But I feel very fortunate for all of us to have walked away with the best picture award. It’s pretty remarkable.”